Module 2 Flashcards
What’s in the centre of an atom?
protons and neutrons which make up the nucleus
What orbits the nucleus?
electrons in shells
give the relative mass of all subatomic particles
proton=1
neutron=1
electron=1/2000
give the relative charges of all subatomic particles
proton= +1
neutron= 0
electron =-1
atomic number?
number of protons.
also number of electrons if not charged
mass number?
number of protons and neutrons in nucleus
isotope?
atoms of the same element with different numbers of neutrons
what do isotopes of the same element have?
- different masses
- same number of protons and electrons
- different numbers of neutrons in nucleus
why do different isotopes of the same element react in the same way?
because:
- it’s the number and arrangement of electrons that decides the chemical properties of an element and isotopes have the same configuration so the same chemical properties.
- neutrons make no difference to chemical reactivity
what are ions?
an ion is a positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion)
You have an Na+ ion. Give the atomic number Give the mass number Give proton Give neutron Give electron Overall charge?
atomic no =11 mass no=23 p=11 n=12 e=10 overall charge=11-10=1+
You have a Cl- ion. Give the atomic number Give the mass number Give proton Give neutron Give electron Overall charge?
atomic no =17 mass no=35 p=17 n=18 e=18 overall charge= 17-18= 1-
F- is a negative ion
Explain
The negative charge means there’s 1 more electron than there are protons. F has 9 protons so F- must have 10 electrons. The overall charge = +9-10= -1
Mg2+ is a positive ion.
Explain.
The 2+ charge means that there are 2 fewer electrons than there are protons. Mg has 12 protons so Mg2+ must have 10 electrons. The overall charge = +12-10=+2
What did Democritus say about matter?
All matter is made from indivisible particles
What did John Dalton say about matter?
described atoms as solid spheres and that different types of sphere made up different elements
What did JJ Thomson say about matter
1897
-atoms weren’t solid and indivisible
-atom must contain a smaller negatively charged particle “corpuscles” (electrons) so the solid sphere idea of atomic structure had to be changed.
NEW MODEL PLUM PUDDING - A POSITIVELY CHARGED SPHERE WITH NEGATIVE ELECTRONS EMBEDDED IN IT
What did Rutherford say about matter?
1909 Rutherford Geiger and Marsden gold foil experiment.
there’s a tiny positively charged nucleus at the centre of the atom surrounded by a “cloud” of negative electrons. Most of the atoms mass is concentrated at the centre so most of the atom is empty space.
Further Modifications to Rutherford model?
Henry Moseley discovered the charge of the nucleus increased from one element to another in units of one.
Rutherford discovered that the nucleus contained positively charged particles called proton.
The charges of the nucleus of different atoms could be explained because atoms of different elements have a different number of protons in their nucleus
James Chadwick on atomic models
the nucleus of atoms were heavier if they just contained protons
Rutherford predicted there were other particles in the nucleus with mass but no charge
James Chadwick discovers the neutron
Describe in 4 steps, Bohrs atomic model
Niels Bohr:
- Electrons only exist in fixed orbits(shells) and not anywhere in between
- Each shell has a fixed energy
- When an electron moves between shells electromagnetic radiation is emitted or absorbed
- because the energy of shells is fixed, the radiation will have a fixed frequency
What else did the Bohr model explain?
The Bohr model also explained why the noble gases are inert.
He said the shells of an atom can only hold fixed numbers of electrons and an elements reactivity is due to its electrons.
So when an atom has full shells of electrons it’s stable and does not respect.
What’s the most accurate atomic model today?
Involves quantum mechanics- you can never know where an electron is or which direction it’s going in at any moment, but you can say how likely it is to be at a certain point in the atom.
Electrons can act as waves as well as particles.
DEFINE relative atomic mass Ar
The weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon 12 the relative atomic mass of each element is shown in the periodic table.
DEFINE relative isotopic mass
relative isotopic mass is the mass of an atom of an isotope of an element compared to 1/12 of the mass of an atom of carbon 12.
How is relative atomic mass (Ar) of an element calculated from its isotopic abundance’s?
- multiply each relative isotopic mass by its % relative isotopic abundance
- /100
Get a calculator.
Calculate the Ar of boron:
20% of boron atoms have a relative isotopic mass of 10.0 while 80% have a relative isotopic mass of 11.0.
-multiply each relative isotopic abundance and add up the results:
(10.0x20.0) + (80.0x11.0) = 200+880 =1080
divide by 100: 10.8
What is mass spectrometry?
What’s a mass spectrum?
- form of molecular chemical analysis, ions passed through mass spectrometer, ions sorted based on their mass-to-charge ratio.
- a mass spectrum is produced, can be used to identify an unknown compound, provides structural information about the molecule - can determine the relative abundance of each isotope of an element.
VIADD
1. Vaporisation - sample is vaporised before being injected into the mass spectrometer
- Ionisation - vaporised sample is bombarded with electrons in the ionisation chamber
- electrons knock electrons out of the sample
- positive ions are formed
- majority of ions carry +1 charge - Acceleration- beam of ions is accelerated
- Deflection- magnetic field deflects the beam, different ions are deflected by different amounts, degree of deflection depends on mass and charge (lighter ions deflected more and those which carry a bigger charge are deflected more)
- Detection- not all of the ions will reach the detector, some ions may: collide with walls of mass spec, gain electrons and become neutralised. Those that do reach the detector are detected as an electric current, electricity flows when ion hits metal detector box so allows detection of ions.
on a mass spectrum:
y axis?
x axis?
y= abundance of ions often as a %, for an element the height of each peak gives the relative isotopic abundance
x= units given as a mass/charge ratio
add mass spectra example
pic
DEFINE relative molecular mass Mr
The average mass of a molecule compared to 1/12 of the mass of an atom of carbon 12.
To find the Mr just add up the relative atomic mass values of all the atoms in the molecule
Calculate the relative molecular mass of C2H6O
Mr of c2h6o = (2x12) + (6x1) + (1x16) = 46
DEFINE relative formula mass.
Relative formula mass is the average mass of a formula unit compared to 1/12 of the mass of an atom of carbon 12.
It’s used for compounds that ionic or giant covalent.
To find the relative formula mass just add up the relative atomic masses (Ar) of all the ions in the formula unit.
Calculate the relative formula mass of CaF2 and CaCO3
CaF2=
In CaF2 there’s one Ca2+ ion got every 2- ions. Mr if CaF2= 40.1+(2x19)= 78.1
CaCo3=
In CaCo3 there’s one Ca2+ ion for each CO3 2-
Mr= 40.1+12+(3x16)=100.1
What is a mole?
measurement of amount of substance given in symbol n.
one mole is 6.02x1023 particles - the Avogadros constant
it doesn’t matter what the particles are - they can be atoms, molecules,electrons,ions etc.
eg. 2Mg+O2-> 2MgO
2 atoms of magnesium react with 1 molceule of oxygen to make 2 molceules of magnesium oxide
2 moles of magnesium react with 1 mole of oxygen molecules to make 2 moles of magnesium oxide.
What is the formula for finding the number of moles from the number of atoms or molecules?
IF you have 1.50x10^24 carbon atoms how many moles of carbon is this?
Number of moles= number of particles you have/number of particles in a mole
moles= 1.50x10^24 / 6.02x10^23 = 2.49 moles
What is molar mass?
What is the unit for molar mass?
Find the molar mass for Ni(OH)2
Molar mass, M is the mass of one mole of something. Molar mass has the same numerical value as the relative molecular mass, Mr or relative formula mass.
The unit is gmol-1
Ni(OH)2= 58.7+ (2x(16+1))=92.7
M= 92.7 gmol-1 (1 mole of Ni(OH)2 weighs 92.7g)
What formula connects the molar mass of a substance to the number of moles of the substance you have?
`moles = mass of substance/ molar mass
mr mol lives under ground
How many atoms are in 1 mole of Fe?
6.02x1023
Find the molar mass of MgSO4
24.3+32.1+16x4= 120.4gmol-1
How many moles of sodium nitrate are present in 212.5g of NaNO3?
moles=mass/mr
212.5/85=2.5 moles
How many moles of zinc chloride are present in 15.5g of ZnCl2?
MOLES=MASS/MR
12.5/136.4=0.114 moles
what is the mass of 0.25 moles of MgCO3?
mass= molesxMr
21.075g=0.25x (84.3)
How many O2 molecules are in 82.1g of oxygen?
M= 16+16 = 32gmol-1
number of moles= 82.1/32 = 2.565..mol
number of molecules= 2.565… x 6.02x10^23=1.54x10^24
a sample of pure magnesium sulfate, MgSO4, contains 3.56x10^24 atoms. What is the mass of the sample?
number of moles of atoms = 3.56x10^24 x 6.02x10^23
=5.913 mol
MgSO4 = 6 atoms
moles of MgSO4 (using moles you have/moles in compound) = 5.913/6 = 0.985…
M(MgSO4) = 120.4gmol-1 mass = 0.985... x 120.4 = 119g is the mass of the sample
what is molar gas volume?
units?
if temperature and pressure stay the same, one mole of any gas always has the same volume - this is the molar gas volume
units: dm3mol-1
For molar gas volume, what are the values for room temperature and pressure?
temperature= 298K
pressure=100k
molar gas volume=24dm3mol-1 or 24,000cm3.mol-1
Give the 2 formulas for working out the number of moles in a volume of gas - ONLY USE THEM FOR R.T.P!
ONLY USED FOR R.T.P
number of moles= volume in dm3 / 24
OR
number of moles= volume in cm3 / 24,000